1. Field of the Invention
The invention is directed to radar devices and more particularly to (1) special circuits for use in modulated CW or pulse Doppler radar for enabling the radar to distinguish not only the phase differences (Doppler) between returning echo signals from one or more targets but also distinguish amplitude differences between the one or more targets and lock the attention of the radar onto a selected echo signal and continue to monitor that specific target echo so long as that target is of particular interest as determined by the radar system, and (2) special circuits for conditioning selected portions of the Doppler frequency spectrum to attenuate or de-emphasize portions of the echo signal corresponding to selected targets in the radar system environment, such as rain or stationary wayside objects, in order to give such echo signals less weight in determining roadway hazards.
2. Description of Related Art
U.S. Pat. No. 4,673,937 issued to John W. Davis on Jun. 16, 1987 and assigned to the Assignee of the present invention teaches a vehicle borne radar system presently believed to be at the leading edge of the vehicle borne radar art.
However, the above-referenced radar system is not able to distinguish one individual target echo signal from a plurality of incoming target echo signals of approximately the same amplitude and lock on to that particular target echo signal until that target echo signal is replaced by a new particular target echo signal.
There is a continuing need to improve the safety of highway vehicles operation for preventing impact with moving and stationary objects and to safely increase the density of vehicles traveling the world's roadways by monitoring the distance, speed and direction of travel between one vehicle following another thereon to conserve available road space by safely increasing the number of vehicles on a given roadway at any given time and yet maintain a higher than now possible degree of safety for the passengers carded by those vehicles.
The present invention relates to an improved vehicle borne radar system for monitoring possible dangerous conditions for a particular vehicle traveling on a vehicle roadway.
It is also known, as shown for example by U.S. Pat. No. 3,952,303 of Watanabe et al, to transmit and receive at three different frequencies on a time division basis, with two of the frequencies being used to determine range, closing speed and likelihood of collision and the third frequency being combined with one of the first two to determine direction. However, three frequency systems are capable of even further simplification in the circuitry thereof using different techniques of determining the desired information. Moreover, the transmit and receive frames containing the frequencies can be wasteful in that only small portions thereof are needed to receive and segregate the signals of different frequency, with the remaining portions being unused.
There is also a continuing need to condition the return echo signal from an automotive collision avoidance radar system in order to generate meaningful information from a very complex sequence of events. In such a system, the radar system transmits an RF signal outward through an antenna. If an object (target) is present, it reflects the RF signal. A very small part of the reflected signal is returned to the antenna. Target detection runs from very good to non-existent, even when a strongly reflecting target is present. Although radar target back-scatter phenomenon is fairly well understood for distant targets and free space, the multitude of target sizes and shapes near a road surface can cause unusual problems for the processing circuitry of an automotive collision avoidance radar system. In particular, reflections from such environmental targets as rain, as well as non-threatening but strongly reflecting wayside targets such as overpasses, signs, etc. can obscure the information generated from a more threatening target in the environment (such as an on-coming automobile). Therefore, it would be desirable to condition the received Doppler frequency spectrum on a selected basis in order to de-emphasize non-threatening targets in comparison to targets having a higher probability of presenting a threat to a vehicle.